Benzene oxychlorination



June 18, l1968 w. H. PRAHL ETAL. 3,389,186l

BENZENE OXYCHLORINATION Filed Nov. 26, 1965 4 CNN# E 55s of mzmNzmm G:EN 32525335 .F 2:38 2925.55 @QN\ WMS 2J 9N mzmNzmm E2; n.555 Sqv A NN/EN 2-\ f N mj 2J A SEE Qz EEE 252mm m=omoa fom mom United States Patent@mee 3,389,186 Patented June 18, 1968 3,389,186 BENZENE GXYCHLORlNATIONWalter H. Prahl, Buffalo, N.Y., Jay P. Eggert, Bellefonte,

Ashland, Ky., and Sol J. Lederman, Kenmore, Eric H. Scremin, NiagaraFalls, and Albert C. Ullrich, Williamsville, utfalo, N.Y., assignors toHooker Chemical Corporation, Niagara Falls, N.Y., a corporation of NewYork Continuation-impart of application Ser. No. 133,803,

Aug. 2S, 1961. This application Nov. 26, 1965, Ser.

4 Claims. (Cl. 260--650) This is a continuation-inpart of our co-pendingapplications Ser. No. 133,803, tiled Aug. 25, 1961, now abandoned, andSer. No. 292,460, tiled July 2, 1963.

This invention relates to the chlorination of benzene, and morespecifically to the vapor phase chlorination of benzene by means ofhydrogen chloride and an oxygencontaining gas over a catalyst, atelevated temperatures between about two hundred and about three hundreddegrees centigrade.

The vapor phase chlorination of benzene by means of hydrochloric acidand an oxygen-containing gas is carried out essentially for the purposeof producing monochlorobenzene. However, with increasing conversion ofbenzene to monochlorobenzene, increasing quantities of diand more highlychlorinated benzenes are formed. For this reason, it is practicallynecessary to keep the conversions down to around ten to twenty percentper pass, or in other words, to pass through the catalyst an excess ofbenzene vapor of iive to ten times the quantity which is to be reacted.In the conventional method the whole quantity of benzene is firstvaporized with a concurrent consumption of steam, then passed throughthe catalyst together with appropriate quantities of hydrogen chloride,water and air, and then the condensible components of the reactionmixture are condensed with a concurrent consumption of cooling water.The excess benzene is separated, for instance, by distillation, andreturned to the vaporization step for re-use.

An object of the present invention is to provide a more economicalmethod of producing monochlorobenzene by saving some of the heatnormally required to vaporize the excess benzene and some of the coolingwater normally required to condense it.

Another object is to provide a more economical method of producingmonochlorobenzene by permitting the production of a given quantity ofmonochlorobenzene in smaller equipment.

Still another object is to improve the thermal characteristics of thereaction and thereby reduce the tendency of the reaction to lead tocomplete combustion of some benzene to carbon dioxide.

Other objects of the invention will become apparent in the course ofthedescription.

These and other related objects of the present invention are achieved byintroducing the reacted mixture from the catalyst chamber withsubstantially no cooling into the bottom portion of a distillation zoneor column, into the top portion of which benzene and water are fed,thereby utilizing the available heat content of the reacted mixture toevaporate a corresponding quantity of benzene and water in theapproximate composition of the benzenewater azeotrope, thereby forming avaporous mixture comprising water, benzene and inerts at the top of thecolumn, withdrawing the said vaporous mixture, and recirculating aportion of the said benzene-water mixture to the said catalyst chamber.

The percentage of materials which can be returned as feed to thecatalyst chamber in any reaction depends mainly upon the quantity offoreign materials which must be purged from that reactions productstream. The foreign materials to be removed from the stream of thepresent reaction are mainly nitrogen when the oxygencontaining gas usedis air, Water which is introduced with the reactant hydrogen chloride,and small amounts of byproduct carbon dioxide. The quantity of theseforeign materials to be purged is so large that a direct recirculationof the reactants has up to now been impossible, for the reason that itwould interfere with the necessary purging of the large quantities offoreign matter in the system, and thus lead to an unmanageable increasein purge products and an unacceptable dilution of the reactants.

According to the present invention, it was found that if the sensibleheat of the reacted mixture issuing from the catalyst chamber is used tovaporize benzene and water in a ratio of approximately the benzene-waterazeotropic composition, then the composition of the vaporous mixtureissuing from the top of that column is so improved that therecirculation of a substantial portion of it into the reaction can bepermitted without incurring the disadvantages above mentioned. We havefound that from about live percent to about seventy-tive percent of theresultant vaporous mixture can be recirculated to the reaction zone. Amore preferable operating range however, is from about ten percent toabout forty percent of the resultant vaporous mixture.

The improvement in the vapor mixture to be recycled is believed to becaused by two main factors; but we do not Want to be limited to thesetheories, except as dened in the appended claims: (l) A considerablepercentage of the water introduced into the reaction in the form ofabout twenty percent hydrochloric acid and formed in the reaction by thechlorination, together with the chlorinated benzenes, is eliminated atthe bottom of the column. (2) The percentage of purge material in thevaporous mixture issuing from the top of the column is reduced by theaddition to it of the benzene-water mixture having approximately thecomposition of the azeotrope which is vaporized in the column.

The result is that the concentration of the purge gases is suliicientlylow to permit recycling of a portion of it into the reaction.

Referring to the figure, the following description is given tofacilitate an understanding of the invention.

Benzene (liquid) in line 200 is vaporized in benzene vaporizer 201. Thebenzene vapors pass through line 203 to vapor mixer 206, Where air fromline 207 and hydrochloric acid from line 208 are mixed with the benzene.The mixed vapors then pass through line .210v into catalyst chamber 221.The resultant hot reaction gases pass through line 211 withsubstantially no cooling to distillation column 212, where Water andbenzene fed in through line 213 are used to condense out thechlorobenzenes. The liquid chlorobenzenes, benzene and water arewithdrawn through line 220 for further processing. A portion of thevaporous overhead stream in line 214 is withdrawn through line 215 forfurther processing.

In accordance with the instant invention, the remaining portion of thevaporous mixture in line 214 is recirculated in line 218 to thecatalytic reaction zone. The vaporous material in line 218, can bereturned to the beginning of the process and re-introduced at line 203.In addition, the

vaporous effluent stream line 218 can be split with one stream beingre-injected into the system at line 283, while the remaining stream isre-injected through line 219 directly into the reaction gases emergingfrom one catalytic Zone and passing to the next adjacent zone incatalyst chamber 221.

The advantages of this method will be demonstrated by the comparison ofthe following two numerical examples, the rst of which shows theoperation, wherein the sensible heat of the crude reactants is notutilized in accordance with our invention, while the second shows themethod according to this invention. However, we do not ywish to belimited to them except as defined in the appended claims.

Example 1 Benzene at the rate of 10,343 pounds per hour is vaporized andmixed with the vapors of 3169 pounds per hour of 17.3 percenthydrochloric acid, and then passed together with 1545 pounds per hour ofair, at a temperature of about 200 to about 300 degrees centigrade,through a catalyst chamber in a process according to U.S.P. 1,963,761.Table I gives in column l the composition in pounds per hour of thegas-vapor mixture entering the i hydrogen chloride and oxygen, areidentical with those in Example 1.

Likewise, the composition of the crude product mixture leaving thecatalyst chamber corresponds identically with the figures shown in Tablell, column 4, and Table I, column 2, except for the slightly largerwater, nitrogen and carbon dioxide contents.

This reaction product mixture is fed into a distillation column operatedat approximately atmospheric pressure to the top of which are fed thequantities of benzene and water shown in Table Il, column 5. Theavailable heat of the crude product vapor mixture entering the bottom ofthe column is thereby utilized essentially for the vaporization of thebenzene-water azeotrope. We have found that the gas-vapor mixtureissuing from the top of that column has approximately the compositiongiven in Table II, column 6. Thus, the benzene content of this resultantvaporous mixture has been increased to 87.3 percent benzene in Table Il.This enrichment in benzene content in any given case depends on theoriginal composition of the reaction product mixture and its heatcontent, and it may increase the benzene content to values of from about60 percent to about 90 percent, depending on these factors.

TABLE II.PROCESS OF EXAMPLE 2 Starting Material Total Material CrudeProduct Liquid Into Gaseous Ma- Liquid Ma- Material Recycled, IntoCatalyst Into Still, Top of Still, terial Leaving terial Leaving EndProduct, Vaporized, Lb./I:Ir. Chamber, Lb./ Lb./Hr. Lb./Hr. Still,Lim/Hr. Col., Lb./Hr. Lb./Hr.

Lb./Hr. Hr.

Mouochlorobenzene 1, 400 1, 400 1, 400 Dichlorobenzone 140 0 140 6, 7553, 588 10, 343 9, 274 549 549 16 2, 620 328 2, 948 3, 224 1, 140 176 1,316 1, 316 347 10 357 73 9 9 65 Others 14 Total 11, 411 4, 111 15, 52215,522

reaction chamber, and in column 3 the composition of the reactedgas-vapor mixture coming out of the catalyst chamber having atemperature of approximately 300 degrees centigrade.

The product, namely 1400 pounds per hour of monochlorobenzene and 140pounds per hour of dichlorobenzenes, can be isolated by the conventionalmethods such as condensation, distillation, etc. Thus, even if theproducts could be removed without condensing simultaneously any of thebenzene, the percentage of material to be purged (eg. water, nitrogen,and carbon dioxide), would amount to about 35 percent of the mixture,which is much too large for recycling from a practical standpoint.

TABLE I.-PROCESS OF EXAMPLE I Example 2.-Process according to inventionIn the process according to this invention, the total vaporized startingmaterial entering the catalyst chamber as given in Table II, column 3,differs from that used in Example 1 only insofar as slightly more water(2948 pounds per hour instead of 2620 pounds per hour), slightly morenitrogen (1316 pounds per hour instead of 1188 pounds per hour), arepresent. The gures for the other starting materials namely thereactants, benzene,

The material to be purged from the vaporous mixture leaving the top ofthe still (water, nitrogen and carbon dioxide), amounts to only 13.5percent in this stream (as compared to about 35 percent in Example l). Asubstantial portion of it therefore can be profitably recycled.

It is entirely feasible to supply all the benzene to be used in thereaction by recycling a portion of this stream. However, since normallysome benzene -vapor is available from the purication of the product, weprefer to supply only about one-half of the required benzene byrecycling. In the present example as shown in Table II we recycle onlyabout 13.4 percent of this gas stream, giving a recycle stream of thecomposition shown in column 3.

In order to reach the desired composition of the stream entering thecatalyst chamber as given in column 3 of Table II, we vaporize thequantities shown in column 1, namely 3169 pounds per hour of 17.3percent hydrogen chloride with 1487 pounds of air added to it, and wevaporize 6755 pounds per -hour of benzene.

A comparison of these figures with those in Example 1 shows that weobtain essentially the same composition of the reaction mixture and thesame production by vaporizing only 6755 pounds per hour of benzene, ascompared to 10,343 pounds per hour of benzene, in the conventionalprocess.

In addition, we have found that owing to the slightly higher dilutionwith nerts (Water 2948 pounds per hour, against 2620 pounds per hour,and nitrogen 1316 pounds per hour against 1188 pounds per hour), thecombustion taking place in the catalyst chamber, as indicated by theproduction of carbon dioxide, would be actually somewhat lower, and theyield of product correspondingly higher in the process according to thepresent invention than in the conventional process.

Another of the main advantages of our process is the fact that theimproved thermal economy of the process permits a lower conversion perpass, without undue increase in operating expense involved in thevaporization of benzene. This in turn results in a lowered simulta-TABLE IIL-PROCESS OF EXAMPLE 3 Total Crude Gaseous Liquid MaterialMaterial Material Product Liquid Into Material lilaterial End Vaporized,Recycled, Into Catalyst Into Still, Top oi Still, Leaving Still, LeavingCol. Product,

lim/hr. lb./lu. Cllambcr, lb./lir. lb./hr. lb./hr. lb./hr. lb./hr.

.\ i onoclilorobenzene 12, 603 12, 603 Di clilorobenzene 254 254Bou/,eue 353, 369 404, 065 395,062 13, 257 HCL..V 4,335 10G 10S 3l, 27452, 375 54. 512 23, 081

. 22, 853 l, 271 1, 137 Others... 13 13 Total 87, 811 4, 000, 000 487,811 487, 811 339, 718 778, 215 49, 314

neous production of unwanted diand more highly chlorinated benzenes.

Still another advantage is that smaller size equipment may be used toobtain the same results of the conventional process.

The vaporous mixture of water, benzene and inerts being recirculated tothe benzene oxychlorination zone is recirculated to a suitable point inthe overall benzene oxychlorination process where it is re-injected intothe process. A preferred method of this invention is to pass thevaporous mixture with the stream of benzene, HCl, and air into thecatalytic reaction zone, preferably prior to entering the pre-heater.The two streams can be fed separately or together into the pre-heater.This both premixes and pre-heats the materials. Other methods forre-injecting the recirculated vaporous mixture into the process can beused however. For instance, as shown in ouri' said co-pendingapplication Ser. No. 292,460 filed July 2, 1963, `by dividing thecatalyst into at least two packed catalytic zones in series, each ofsaid zones being adapted to cause only a partial conversion of thereactants to monochlorobenzene and to cause an increase in temperatureof the reaction gas stream, and it can be reinjected by introducing atleast some of the vaporous mixture directly into the reaction gas streambetween the catalytic zones in order to cool the reaction gases whilepassing from one catalytic zone to the next adjacent zone. Still othermethods of re-entering the recirculated vaporous mixture into thebenzene oxychlorinaton system may be used. The portion of vaporouseluent being recirculated can be split into a number of streams with onestream re-injected into the system with the stream of benzene, HC1 andoxygen-containing gas, while the re- J mainlng stream or streams bemgre-lnjected elsewhere,

such as directly into the reaction Igases emerging from one catalyticzone and passing to the next adjacent zone.

Example 3.--Process with 51.4% recycled In Example 2, about 13.4 percentof the vaporous eiuent from t-he distillation column is recirculated.(This is calculated from Table II -by dividing- 3588 in column 3 by26,888 in column 7 of Table 1I and multiplying by 10Q.) The followingexample is given to further illustrate the invention, by showing inTable III a process wherein about 51.4 percent of the vaporous eiiluentfrom the distillation column is recirculated to the beginning of thebenzene oxychlorination process and passed with the benzene, HC1 and airinto the catalytic reaction zone. (This percentage is calculated fromTable III by dividing 400,000 in column 3 by 778,215 in column 7 andmultiplying by 100.) The figures in Table III are based Although in theexamples herein the distillation column is operated at approximatelyatmospheric pressure, pressures above or below this may also be usedwithout departing from the scope of our invention.

Since various modifications to this process can be made by one ofordinary skill in this art without departing from the scope of theinvention, we do not want to be limited hereto except as defined in theappended claims.

We claim:

1. In a continuous process for the production of monochlorobenzene,wherein vapors of benzene, hydrogen chloride and an oxygen-containinggas are passed through a catalytic reaction zone, the reacted mixture iswithdrawn therefrom and introduced with substantially no cooling intothe bottom portion of a distillation zone wherein benzene and water arebeing introduced into the top portion thereof, thereby utilizing theavailable heat content of the said reacted mixture to evaporate acorresponding quantity of a benzene-water mixture having approximatelythe composition of the benzene-water azeotrope, thereby forming andwithdrawing a vaporous mixture comprising water, benzene and inerts atthe top portion of the distillation zone, the improvement whichcomprises: recirculating from about five percent to about seventy-tivepercent of said vaporous mixture to the said catalytic` reaction zone.

2. The process according to claim 1 wherein from about ten percent toabout forty percent of the vaporous mixture is recirculated.

3. The process according to claim 1 wherein the recirculated vaporousmixture is passed with the said benzene, hydrogen chloride and anoxygen-containing gas into the catalytic reaction zone.

4. The process according to claim 1 wherein the recirculated vaporousmixture is split into a number of streams with one stream re-injectedinto the system with the said benzene, hydrogen chloride, and anoxygencontaining gas into the catalytic reaction zone.

References Cited UNITED STATES PATENTS 1,963,761 6/1934 Prahl 260--650 X2,126,988 '8/19'38 Engelstein 208-81 2,166,829 7/1939 Swartwood 208-812,827,502 3/1958 Loeser et al. 260-650 BERNARD HELFIN, Acting PrimaryExaminer.

LEON ZITVER, Examiner.

H. T. MARS, N. J. KING, Assistant Examiners.

1. IN A CONTINUOUS PROCESS FOR THE PRODUCTION OF MONOCHLOROBENZENE,WHEREIN VAPORS OF BENZENE, HYDROGEN CHLORIDE AND AN OXYGEN-CONTAININGGAS ARE PASSED THROUGH A CATALYTIC REACTON ZONE, THE REACTED MIXTURE ISWITHDRAWN THEREFROM AND INTRODUCED WITH SUBSTANTIALLY NO COOLING INTOTHE BOTTOM PORTION OF A DISTILLATION ZONE WHEREIN BENZENE AND WATER AREBEING INTRODUCED INTO THE TOP PORTION THEREOF, THEREBY UTILIZING THEAVAILABLE HEAT CONTENT OF THE SAID REACTED MIXTURE TO EVAPORATE ACORRESPONDING QUANTITY OF A BENZENE-WATER MIXTURE HAVING APPROXIMATELYTHE COMPOSITION OF THE BENZENE-WATER AZEOTROPE, THEREBY FORMING ANDWITHDRAWING A VAPOROUS MIXTURE COMPRISING WATER, BENZENE AND INERTS ATTHE TOP PORTION OF THE DISTILLATION ZONE, THE IMPROVEMENT WHICHCOMPRISES: RECIRCULATING FROM ABOUT FIVE PERCENT TO ABOUT SEVENTY-FIVEPERCENT OF SAID VAPOROUS MIXTURE TO THE SAID CATALYTIC REACTION ZONE.